Conversion of hydrocarbons



Reissued May 28, 1940 UNITED STATES PATENT OFFICE conversion or mnocmous'No Drawing. Original No. 2,124,584. m July as, 193s, Serial No.103,394. September so, me.

Application for Serial No. 295,108

8Claims.

This invention relates particularly to the conversion of straight chainhydrocarbons into closed chain or cyclic hydrocarbons.

More specifically it is concerned with a process" involving the use ofspecial catalysts and specific conditions of operation in regard totemperature, pressure and time of reaction whereby aliphatichydrocarbons'can be eificiently converted into aromatic hydrocarbons.

10 In the straight pyrolysis of pure hydrocarbons or hydrocarbonmixtures such as those encountered in fractions from petroleum or othernaturally occurring or synthetically produced hydrocarbon mixtures thereactions involved I it which produce aromatics from paraillns andolefins are of an exceedingly complicated charac+ ter and cannot be veryreadily controlled.-

It is generally recognized that, in the thermal decomposition ofhydrocarbon compounds or $0 hydrocarbon mixtures of relatively narrowrange that whateverintermediatereactions are involved,

there is an overall loss of hydrogen, a tendency to carbon separationand a generally widerboiling range in the total liquid products as com-I pared with the original charge. Under mild cracking conditionsinvolving relatively low temperatures and pressures and short times ofexposure to cracking conditions it is possible to some extent to controlcracking reactions-so that a they are limited to primary decompositionsand there is a minimum loss of hydrogen and a maximum production of lowboiling fractions consisting of compounds representing the fragments ofthe original high molecular weight compounds.

As the conditions of pyrolysis are increased in severity using highertemperatures and higher times of exposure to pyroly'tic conditions,there is a progressive increase in loss of hydrogen and a large amountof secondary reactions involving recombination of primary radicals toform polymers and some cyclization to form naphthenes and aromatics, butthe mechanisms involved in these cases are of so complicated a naturethat very little positive information has been evolved in spite of thelargeamount of experimentation which has been done and the large numberof theories proposed. In general, how-. ever, it may be said thatstarting with paramn hydrocarbons representing the highest degree ofsaturation that these compounds are changed progressively into oleflns,naphthenes, aromatics, and finally into carbon and hydrogen and otherlight fixed gases. It is not intended to infer from this statement thatany particular success has reissue September 15, 1939,

attended the conversion of any given paramn or, other aliphatichydrocarbon into an aromatic hydrocarbon of the same number of carbonatoms by way of the progressive steps shown. If this is done it isusually with very low yields which are ii of very little practicalsignificance.

The search for catalysts to specifically control and 'accelerate desiredconversion reactions among hydrocarbons has'been attended with the usualdifiiculties encountered in finding catalysts 10 for other types ofreactions since there are no. basic laws or rules for predicting theefi'ectiveness of catalytic materials and the art as a whole is in amore or less empirical state. In using catalysts even in connection withconversion reactions among pure hydrocarbons and particularly .inconnection with the conversion of the relatively heavy distillates andresidua which are available for cracking, there is a general tendencyfor the decomposition reactions to proceed at $0 a very rapid rate,necessitating'the use of extremely short time factorsv and very accuratecontrol of temperature and pressure to avoid too extensivedecomposition. There are further diiliculties encountered in maintainingthe ei'flcien- :5 cy of catalysts employed in pyrolysis since there isusually a rapid deposition of carbonaceous materials on their surfacesand. in their pores.

The foregoing brief review of the art of hydrocarbonpyrolysis is givento furnish a general 80 background for indicating the improvement insuch processes which is embodied in the present invention, which may beapplied to the treatment of pure parafin or olefin hydrocarbons,hydrocarbon mixtures containing substantial per- 86 centages of paraflinhydrocarbons such as relatively close out fractions producible bydistilling petroleum, and analogous fractions which conselected fromthose occurring in the lefthand column of Group V of the periodic table,these compounds having relatively high catalytic activity. I

According to the present invention aliphatic or straight chainhydrocarbons having 6 or more carbon atoms in chain arrangement in theirstructure are specifically dehydrogenated in such a way that the chainof carbonatoms undergoes ring closure with the production in thesimplest case of benzene from n-hexane or n-hexene and in the case ofhigher molecular weight parafllns of various alkyl derivatives ofbenzene. Under properly controlled conditions of times of contact,temperature and pressure very high yields of the order of 75.to 90% ofthe benzene or aromatic compounds are obtainable which are far in excessof any previously obtained in the art either with or without catalysts.For the sake of illustrating and exemplifying the types of hydrocarbonconversion reactions which are specifically accelerated under thepreferred conditions by the present types of catalysts, the followingstructural equations are introduced:

OH: CH cm OH: I in on g, cm on cn CH: CH

n-hexane bomene om c-crn CH: CHI-CHI I ('33 (FE HH 1 our ca on cm onn-heptane toluene /CH: /C{ CH: CBr-CH: I (In C-CH; +43 Cg: CHr-CH: CE-CH| H: on

n-octane o-xylene In the foregoing table the structural formulas of theprimary paramn hydrocarbons have been represented as a nearly closedring instead of by the usual linear arrangement for the sake ofindicating the possible mechanisms involved. No-

attempt has been made to indicate the possible intermediate existence ofmono-olefins, diolefins,

hexamethylenes or alkylated hexamethylenes tions involved but in thecase of n-paramns or mono-olefins of higher molecular weight than theoctane shown and in the ease of branch chain compounds which containvarious alkyl substitucnt groups in different positions along thesixcarbon atom chain, more complicated reactions will bcinvolved. Forexample, in the case of such .a primary compound as 2,3-dimethyl hexanethe principal resultant product is apparently o-xylene although thereare concurrently produced definite yields of such compounds as ethylbenzene indicating an isomerization of two substituent methyl groups. Inthe case of nonanes which are represented by the compound2,3,4-trimethyl hexane, there is formation'not only of mesitylene butalso of such compounds as methyl ethyl benzol and various propylbenzols.

It will be seen from the foregoing that th scope of the presentinvention is preferably limited to the treatment of aliphatichydrocarobns which contain at least 6 carbon atoms in straight chainarrangement. In the case of paramn hydrocarbons containing less than 6carbon atoms in linear arrangement, some formation of aromatics may takeplace due to primary isomerization reactions although obviously theextent of these will vary considerably with the type of compound and theconditions of operation. The process is readily applicable to parafiinsfrom hexane up to dodecane and their corresponding olefins. Withincrease in molecular weight beyond this point the percentage ofundesirable side reactions tends to increase and yields of the desiredalkylated aromatics decrease in proportion.

The present invention is characterized by the use of a particular groupof composite catalytic materials which employ as their base catalystscertain refractory oxides and silicates which in themselves may havesome slight specific catalytic ability in the dehydrogenation andcyclization reactions but which are improved greatly inthis respect bythe addition of certain promoters or secondary catalysts in minorproportions.

.These base supporting materials are preferably of a rugged andrefractory character capable of withstanding the severe use to which thecatalysts are put in regard to temperature during service and inregeneration by means of air 'or other oxidizing gas mixtures after theyhave become-fouled with carbonaceous deposits after a period of service.As examples of materials which may be employed in granular form assupports for the preferred catalytic substances may be mentioned thefollowing:

Montmorillonite clays Kieselguhr Crushed firebrick Crushed silicaMagnesium oxide Aluminum oxide Bauxite Bentonite clays Glauconite(greensand) It should be emphasized that in the field of catalysis therehave been very few rules evolved which will enable the prediction ofwhat materials will catalyze a given reaction. Most of the catalyticwork has been done on a purely empirical basis, even though at timescertain groups of elements or compounds have been found to be more orless equivalent in accelerating certain types of reaction.

In regard to the base catalytic materials which are preferably employedaccording to the present invention, some precautions are necessary toinsure that they possess proper physical and chemical characteristicsbefore they are impregnated with the promoters to render them moreeflicient. In regard to magnesium oxide, which may be alternativelyemployed, this is most conveniently prepared by the calcination of themineral magnesite which is most commonly encountered in a massive orearthy variety and rarely in crystal form, the crystals being usuallyrhombohedral. In many natural magnesites the magnesium oxide may bereplaced to the extent of several percent by ferrous oxide. The mineralis of quite common occurrence and readily obtainable in quantity at areasonable figure. The pure compound begins to decompose to form theoxide at a temperature 5f'350 0., though the rate ofdecomposition onlyreaches a practical value at considerably higher temperatures, usuallyof the order of 800 C., to 900 C. Magnesite is related to dolomite, themixed carbonate of calcium and magnesium,

which latter mineral, however, is not of as good service as therelatively pure magn'eflte in the present instance. Magnesium carbonateprepared by precipitation or other chemical methods may be usedalternatively in place of the natural mineral, as a more reactiveconstituent of carriers consisting of spacing materials of relativelyinert character and in some cases allowing the production of catalystsof higher emciency and longer life. It is not necessary that themagnesite be completely converted to oxide but as a rule it ispreferable that the conversion be at least over 90%, that is, so thatthere is less than 10% of the carbonate remaining in the ignitedmaterial.

Aluminum oxide which is generally preferable as a base material for themanufacture of catalysts for the process may be obtained from naturalaluminum oxide minerals or ores such as bauxite or carbonates such asdawsonite by proper calcination, or it may be prepared'by precipitationof aluminum hydrate from solutions of aluminum sulfate or diflerentalums, and dehydration of the precipitate of aluminum hydroxide by heat,and usually it is desirable and advantageous to further treat it withair or other gases, orbyother means to activate it prior to use.

Two hydrated oxides or aluminum occur in nature, to-wit. bauxite havingthe formula Al2Oa.2Hz0 and diaspore AlzOaJhO. In both of these oxidesiron sesqui-oxide may partially replace the alumina. These two mineralsor corresponding oxides produced from precipitated alu- .minum hydroxideare particularly suitable for the manufacture of the present type ofcatalysts and in some instances have given the best results of any ofthe base compounds whose use is at present contemplated. The mineraldawsonite having the formula NaaAl(Ca)a.2Al(0I-I)a isanother mineralwhich may be used as a source of aluminum oxide.

It is best practice in the final steps of preparing aluminum oxide as abase catalyst to ignite for some time at temperatures within the sameapproximate range as those employed in the ignition of magnesite,to-wit, from IZOD-900 C. This probably does not correspond to completedehydration of hydroxides but apparently gives a catalytic material ofgood strength and porosity so that it is able to resist for a longperiod of time the deteriorating eflects of the service and regenerationperiods to which it is subjected. In the case of the clays which mayserve. as'base catalytic materials for supporting promoters, the bettermaterials are those which have been acidtreated to render them moresiliceous. These may be pelleted or formed in any manner before or afterthe addition of the promoter catalyst since ordinarily they have a highpercentage 01 fines. The addition of certain of the promoters, however,exerts a binding influence so that the formed materials may be employedwithout fear of structural deterioration in service.

Our investigations have also definitely demonstrated that the catalyticefliclency of such substances as alumina, magnesium oxide, and clayswhich may have some catalytic potency in themselves is greatly improvedby the presence of compounds of the preferred elements in relative 1yminor amounts, usually of the order of less than by weight of thecarrier. It is most common practice to utilize catalysts comprising 2 to5% by weight of these compounds, particularly their lower oxides.

The promoters which are used in accordance with the present invention toproduce active catalysts from the base materials include generallycompounds and more particularly oxides of the elements in the lefthandcolumn of Group V of the periodic table including vanadium, columbiumand tantalum. In general practically all of the compounds of thepreferred elements will have some catalytic activity though as a rulethe oxides and particularly the lower oxides are the best catalysts.Catalyst composites may be prepared by utilizing the soluble compoundsof the V Vansnrrm Catalysts comprising 2 to 5 percent by weight of thelower oxides of vanadium such as the sesquioxide V20: and the tetroxideV204 may be used. Some of the monoxide V0 may be present in someinstances. The oxides mentioned are particularly emcient as catalystsfor the present types of reactions but the invention is not limited totheir use but may employ other compounds of vanadium. Thus solutions ofthe ammonium and the alkali metal vanadates may be employed to addvanadium compounds to the carriers and also the soluble vanadyl sulfatesand the'vanadium nitrate and carbonate. The alkaline earth vanadates maybe mixed mechanically and also the halides of vanadium. The oxides perse or those produced by reduction or decomposition of other vanadiumcompounds are preferred.

Conummm A properly prepared carrier may be ground and sized to producegranules of relatively small mesh of the approximate order of from 4 to20 and.

'tioned having the formula CbOF2.2KF.H2O,

which is sumciently soluble in water to render it utilizable as a sourceof columbium catalyst. Other soluble compounds which may be used to formsoluble compounds which may be used to form catalytic depositscontaining columbium are the various alkali metal columbates. Stillother compounds of columbic acids, including salts of the alkaline earthand heavy metals, may be distributed upon the carriers by mechanicalmixing either in the wet or the dry condition. As a rule the loweroxides are the best catalysts. The

oxide resulting from the decomposition of suchcompounds as thepentahydroxide is for the most .part the pentoxide CbrOs. This oxide,however,

is reduced to a definite extent by hydrogen or- TANTALUH Compounds oftantalum, such as for example, the pentoxide Tazos and the tetroxideTazOa. and possibly the sesquioxide TazOa, which result from thereduction of the pentoxide are particularly eflicient as catalysts forthe present types of reactions but the inventionis not limited to theiruse but may employ any of the catalytically active compounds oftantalum. Tantalum fluoride and the double fluoride of tantalum andpotassium having the formula TaKzFv are soluble in water and may beconveniently used in aqueous solution as ultimate sources of the oxideswhich result from the ignition of the precipitated hydroxide to form thepentoxide and the partial reduction of this oxide by hydrogen or thegases and vapors in contact with the catalyst in the normal operation ofthe process. The tantalum pentahydroxide may be precipitated from asolution of the double fluoride by the use of ammonium or alkali metalhydroxides or carbonates as precipitants, the hydrate being laterignited to'form the pentoxide, which may undergo some reduction asalready stated.

The most general method for adding promoting materials to the preferredbase catalysts, which if properly prepared have a high-adsorptivecapacity, is to stir the prepared granules of from approximately 4 to 20mesh into solutions of salts which will yield the desired promotingcompounds on ignition under suitable conditions. In some instances thegranules may be merely stirred in slightly warm solutions of saltsuntilthe dissolved compounds have been retained on the particles byabsorption or occlusion, after which the par-' ticles are separated fromthe excess solvent by settling or filtration, washed with watertor.emove excess solution, and then ignited to produce the desiredresidual promoter. In cases of certain compounds of relatively lowsolubility it may be necessary to add the solution in successiveportions to the adsorbent base catalyst with intermediate heating todrive off solvent in order to get the required quantity of promoterdeposited uponthe surface and in the pores of the base catalyst. Thetemperature used for drying and calcining after the addition of thepromoters from solutions will depend entirely upon the individualcharacteristics of the compound added and no general ranges oftemperature can be given for this step.

In some instances promoters may be deposited from solution by theaddition of precipitants which cause the deposition of precipitates uponthe catalyst granules. As a rule methods of mechanical mixing are notpreferable, though in some instances in the case oi hydrated or readilyfusible compounds these may be mixed with the proper proportions of basecatalysts and uniformly distributed during the condition of fusing orfluxing. T

In regard to the relative proportions of base catalyst and promotingmaterials it may be stated in general that the latter are generally lessthan by weight of the total composites. The eflect upon the catalyticactivity of the base catalysts caused by varying the percentage of anygiven compound or mixture of compounds deposited thereon is not a matterfor exact calculation but more one for determination by experiment.Frequently good increases in catalytic effectiveness are obtainable bythe deposition of as low as 1% or 2% of a promoting compound upon thesurface and'in the pores of the base catalyst,

though the general about 5%.

It has been found essential to the production of high yields ofaromatics from aliphatic hydrocarbons when using the preferred types ofcataaverage is lysts that depending upon the aliphatic hydro-1 carbon ormixture'of hydrocarbons being treated, temperatures from 400-700 0.,should be employed, contact times of approximately 6 to 50 seconds andpressures approximately atmospheric: The use of subatmospheric pressuresof the order of A atmosphere may be'beneficial in that reduced pressuresgenerally favor selective dehydrogenation reactions but on the otherhand moderately superatmospheric pressures usually of the ,order of lessthan 100 pounds per square inch tend to increase the capacity ofcommercial plant equipment so that in practice a balance is struckbetween these two factors. The times of contact most! commonly employedwith n-parafllnic or mono-olefinic hydrocarbons having from 6-12 carbonatoms to the molecule are of the order of 6-20 secs. Itwill beappreciated by those familiar with the art of hydrocarbon conversion inthe presence of catalysts that the factors of temperature, pressure andtime will frequently have to be adjusted from the results ofpreliminaryexperiments to produce the best results in any giveninstance. The criterion of the yield of aromatics will serve to fix thebest conditions of operation. In a general sense the relations betweentime, temperature and pressure are preferably adjusted so that ratherintensive conditions are employed of sufllcient severity to insure amaximum amount of the desired cyclization reactions with a minimum ofundesirable side reactions. If two short times of contact are employedthe conversion reactions will not proceed beyond those of simpledehydrogenation and the yields of olefins and dioleflns willpredominateover those of aromatics.

While the present process is particularly applicable to the productionof the corresponding aromatics from an aliphatic hydrocarbon .or a

- feasible on a basis of concentration, the aromatics produced in thehydrocarbon mixture may be recovered as such by distillation intofractions of proper boiling range followed by chemical treatment withreagents capable of reacting selectively with them. Another method ofaromatic concentration will involve the use of selective solvents suchas liquid sulfur dioxide, alcohols.

furfural, chlorex, etc.

In operating the process the general procedure is to vaporizehydrocarbons or mixtures of hydrocarbons and after heating the vapors toa suitable temperature within the ranges previously specified, to passthem through stationary masses of granular catalytic material invertical cylindrical treating columns or banks of catalyst-containingtubesin p'arall'el connection. Since the reactions are endothermic itmay be necessary to apply some heat externally 'to maintain the bestreaction temperature. Afterpassing through the catalytic zone theproducts are submitted to fractionation to recover cuts or fractionscontaining the desired aromatic product with the separation of fixedgases, unconverted hydrocarbons and heavier residual materials, whichmay be disposed istlc of the present invention.

It is an important feature of the present proccss that the vaporsundergoing dehydrogenation should be free from all but traces of watervapor since the presence of any substantial amounts of steam reduces thecatalytic selectivity of the 1 composite catalysts to a marked degree.In view of the empirical state of the catalytic art, it is not intendedto submit a complete explanation of the reasons for the deleterious,influence of water vapor on the course of the present type of catalyzedreactions, but it may be suggested that the action of the steam is tocause a partial hydration of such basic carriers as alumina andmagnesium oxide and some of the active catalytic compounds due topreferential adsorption so that in eflect the hydrocarbons are preventedfrom reaching or being adsorbed by the catalyticaliy active surface. IThe present types of catalysts are particularly effective in removinghydrogen from chain compounds in such a way that cyclization may bepromoted without removal of hydrogen from end carbon atoms so that bothend and side alkyl groups may appear as substituents in benzene ringsand it has been found that under proper operating conditions they do nottend to promote any great amount of undesirable side reactions leadingto the deposition of carbon or carbonaceous materials and for thisreason show reactivity over relatively long periods of time. when theiractivity begins to diminish after a period of service, it is readilyregenerated by the simple expedient of oxidizing with air or otheroxidizing gas at a moderately elevated temperature, usually within therange employed in the dehydrogenation and cyclization reactions. Thisoxidation effectively removes traces of carbon deposits whichcontaminate the surface of the particles and decrease their efilciency.It is characteristic of the present types of catalysts that they may berepeatedly regenerated with only a very gradual loss of catalyticefliciencyr During oxidation with air or other oxidizing gas mixture inregenerating partly spent material, there is evidence to indicate thatwhen the lower oxides are employed, they are to a large extent, if notcompletely, oxidized to higher oxides which combine with basic carriersto form compounds of variable composition. Later these compounds are dby contact with reducing gases in the first stages of service to reformthe lower oxides and regenerate the real catalyst and hence thecatalytic activity.

' Example I A n-hexane charge obtained by the careful fractionation of aPennsylvania crude oil was found to havea boiling point of 68.8 0., anda refractive index of 1.3768 which corresponds closely to the propertiesof the pure compound.

This material was vaporized and passed over aparts by weight of a 10-12mesh activated alumina. After the addition of the first half of thesolution the particles were somewhat damp and were dried at a steamtemperature to remove excess water. After the heating the second half Iof the solution was added and the dehydration repeated. During theheating period ammonia and water were evolved leaving vanadium pentoxidedeposited on the alumina particles.

The final steps in the preparation of the catalyst comprised heating at200-250-C., for several hours, adding the particles to a catalystchamber in which they were brought up to the necessary reactiontemperature in a current of air, and then subjecting them to the actionof hydrogen at the operating temperature to produce the lower oxides,this change being accompanied by a change in color from yellow to bluishgray.

The yield of pure benzene from the n-hexane when using a temperature of510 C., substantially atmospheric pressure and a time of contact of17.secs., was approximately 48%' by weight of the n-hexane charged as aresult of the single passage over the catalyst. By proper fractionationof the products and recycling of the unconverted material the ultimateyield of benzene was finally brought to approximately 78%.

Example 11 Example Ill The general procedure in the manufacture of thecatalyst was to dissolve the mixed fluoride of potassium and columblumin water and utilize this solution as a means of adding columbiumcompounds to a carrier. A saturated solution of this salt was made up inabout 50 parts of water and this solution was then added to about 250parts by weight of activated alumina which had beenproduced by calciningbauxite/at a temperature of about 700 C., following by grinding andsizing to produce particles of approximately 8-12 mesh. Using theproportions stated the alumina exactly absorbed the solution and theparticles were first'dried at C., for about 2 -hours and the temperaturewas then raisedto 350 C., in a period of 8 hours. After this calciningtreatment the particles were placed in a reaction chamber and theresidual compounds heated in a current of hydrogen at about 500 C., whenthey were then ready forv service.

n-I-Iexane was vaporized and passed over the granular catalyst, using atemperature of 515' 0., substantially atmospheric pressure, and a timeof contact of 18 secs. The yield of pure benzene ,under these.conditions was found to be 46% by weight of the normal n-hexane charged.By recycling of the unconverted material the ultimate yield of benzenewas raised .to 76%.

Example 1v n-Heptane was treated with the same type of catalyst as inExample 111 at a temperature of 565 (2., substantially atmosphericpressure and 10 secs. contact time. The yield of toluene on aonce-through basis was found to be 46% by weight and again it was foundthat by recycling the unconverted n-heptane the yield of the desiredtoluene could ultimately be brought to 76%.

Example V on account of the known difliculty in reducing tantalum oxidealthough some reduction evidently took place when the hydrocarbon gaswas passed over'the mass in the first stages of the treatment.

The n-hexane described above was vaporized and passed over a granularcatalyst comprising the alumina base supporting about 4% by weight oftantalum sesquioxide, using a temperature of 520 C., substantiallyatmospheric pressure, and a time of contact of 19 secs. The yield ofpure benzene under these conditions was found to be 45% by weight of thenormal n-hexane charged. By recycling 0! the unconverted material theultimate yield of benzene was raised to Example VI the unconvertedn-heptane that the yield 01' the desired toluene could ultimately bebrought to 75%.

Example VII To illustrate the results obtainable in the directdehydrogenation and cyclization of oleflns using catalysts according tothe present invention, the conversion of l-hexene into benzol using avanadium oxide on alumina catalyst prepared generally in accordance withthe method given in Example I may be cited.- The vapors of the n-hexenewere passed over the catalyst at a temperature of approximately 510 C.,at atmospheric pressure at a rate corresponding to a total contact timeof approximately 20 seconds, which produced a once-through yield of 72%benzol which could be raised to about by recycling of unconvertedolefln..

Example VIII valyst employed was a mixture of columbium oxides onalumina and was prepared in general accordance with the. procedureoutlined in Example III. At a temperatureof 505 6., substantiallyatmospheric pressure and a time of contact of about 18 seconds, therewas produced a yield of toluene equal in weight to about 74% of then-heptene charged. Recycling again in- 'creasedtheoverallyieldto90%.

We claim as our invention: 1. A process for the. production ofhydrocarbons from aliphatic hydrocarbons 01 from six to twelve carbonatoms. which comprises dehydrogenating and cyclicizing the allphatichydrocarbon by subjection to a temperature of the order of 400 to 700C., for -a period of about 6 to 50 seconds, in the presence of acompound of a.metal from the left hand column of group V of the periodictable and selected from the class consisting of vanadium, columbium andtantalum,

2. A process for the production of aromatic hydrocarbons from aliphatichydrocarbons 01 from six to twelve carbon atoms, which comprisesdehydrogenating by subjection to a temperature of ,the order of 400 to700 C., for a period 01' about 6 to 50 seconds, in the presence of anoxide of a metal from the left hand column of group V oi the periodictable and selected from the class consisting of vanadium. columbium andtantalum.

3'. A process for the production of aromatic hydrocarbons fromaliphatic. hydrocarbons 01 from six to twelve carbon atoms, whichcomprises dehydrogenating and cyclicizing the allphatic hydrocarbon bysubjection to a temperature of the order of 400 to 700 0., for a periodof about 6 to 50 seconds, in the presence of a solid granular catalystcomprising essentially a major proportion of a carrier of relatively lowcatalytic activity supporting a minor proportion of acompound of a metalfrom the left hand column of group V of the periodic table. and selectedfrom the class consisting of vanadium; columbium and tantalum.

4. A process for the production of aromatic hydrocarbons from aliphatichydrocarbons of from six to twelve carbon atoms, which comprisesdehydrogenating and cyclicizing the aliphatic hydrocarbcn by subjectionto a temperature of'the order of 400 to 700 C., for a period of about 6to 50 seconds, in the presence of a, solid granular catalyst comprisingessentially -a major proportion 01' a carrier of relatively lowcatalytic activity supporting a minor proportion of an oxide of a metalfrom the left hand column of group V of the periodic table and selectedfrom the class consisting of vanadium. columbium and tantalum.

5. A process for the production of aromatic hydrocarbons tromyaliphatichydrocarbons 'of from six to twelve carbon atoms, which comprisesdehydrogenating'and cyclicizingzthe aliphatic hydrocarbon by subjectionto a temperature of the order of 400 to 700 C.,.1'or a time period 01'less than 50 seconds but suilicient to dehydrogenate and cyclicize thealiphatic hydrocarbon, in the presence of a compound of a metal from theleft hand column of group V of the periodic table and selected from theclass consisting of vanadium, columbium and tantalum.

6. A process for the production of aromatic hydrocarbons from aliphatichydrocarbons of from six to twelve carbon atoms, which comprisesdehydrogenating' by subjection to a temperature of drocarbons-fromaliphatic hydrocarbons of from six to twelve carbon atoms, whichcomprises dehyd osenatins andcycliciaing the aliphaticbydrocarhonbysubjectiontoatemperatureofthell order of 400 to 700 0., fora time period of less than 50 seconds but suiiicient to dehydrogenateand cyclicize the aliphatic hydrocarbon, in the presence or a solidgranular catalyst comprising essentially a major proportion of a carrierof relatively low catalytic activity supporting a minor proportion 01 acompound 01' a metal from the left hand column of group V oi theperiodic table and selected from the class consisting of vanadium,columbium and tantalum.

8. A process ior the production of aromatic hydrocarbons from aliphatichydrocarbons of from six to twelve carbon atoms, which comprisesdehydrogenating and cyclicizing thealiphatic hydrocarbon by subjectiontoa temperature of the order of 400 to 700 C., for a time period of lessthan 50 seconds but suflicient to dehydrogenate and cyclicize thealiphatic hydrocarbon, in the presence of a solid granular catalystcomprising essentially a major proportion of a carrier of rela-' tivelylow catalytic activity supporting a minor proportion of an oxide of ametal from the left hand column of group Vol the periodic table andselected from the class consisting of vanadium, 1o

columbium and tantalum.

JACQUE C. MORRELL. ARISTID V'. GROSSE.

